1. Technical Field
The disclosure relates to lighting systems with backup power supplies and, more particularly, to emergency lighting systems with centralized backup power, periodic testing systems and methods, and reporting and monitoring systems and methods.
2. Background Information
Emergency lighting products in the USA and other countries are required to be installed in all commercial, industrial and other buildings with public access. Regulations controlling operation and performance of emergency lighting products in the USA are published by the National Fire Protection Association Life Safety Code No. 101, Chapter 7, Means of Egress (LSC 101). Periodic testing of such equipment is required and described in the LSC 101, and is enforced by the Authority Having Jurisdiction (AHJ). The Life Safety Code names four key elements that must be included in every emergency lighting product using batteries to provide stored energy for emergency lighting following loss of main building power:
1. Battery capacity
2. Lamp operation
3. Transfer switch operation
4. Battery charger operation
Testing of all four items is to be performed monthly by simulating a brief loss of main building power, and annually starting 12 months after installation, when emergency operation under battery power for the full rated time is required, commonly 90 minutes but may be longer for certain building occupancies. Results of these tests are to be recorded in permanent written record, to be available for inspection by the AHJ.
Three approved methods for performing the four tests are described in LSC 101, including one describing a computer-based, automated system to minimize the amount of manual labor required, to maintain a history of tests completed, and to produce written test results on demand. Paragraph 7.9.1.3 of LSC 101 contains the following wording: Computer based, self-testing/self diagnostic battery-operated emergency lighting equipment capable of providing a report of the history of tests and failures at all times.
Given the number of fixtures required in typical commercial and industrial buildings, a manual inspection process meeting the requirements for the four tests identified above is labor intensive. With conventional emergency lighting fixtures, monthly and annual tests are accomplished by activation of emergency lighting by pressing a Push to Test (PIT) momentary switch on every fixture. This simulates loss of normal power for as long as the PIT is held down. LSC 101 requires this operation for 30 seconds on every fixture, every month. Results from the test are to be recorded in writing, and the report must be available for inspection by the AHJ at any time. Completion of these tests and reports is an onerous procedure and is rarely accomplished correctly or completely by facility or maintenance managers.
Emergency lighting is required to operate upon loss of normal building power typically supplied by a utility as Alternating Current (AC). Power for emergency lighting must be provided from an independent source, usually batteries, or an electrical generator. The two most common forms of emergency lighting in use today are:
1. Unit equipment, defined as an emergency lighting fixture with a self-contained battery pack, a battery charger and a transfer switch to supply Direct Current (DC) electrical power from the battery for emergency lighting operation upon loss of building power.
2. A central or smaller inverter, defined as a power system that typically includes multiple batteries, a battery charger, a control circuit to convert power supplied by batteries from DC into AC, and a transfer switch to supply this AC power for emergency operation of any standard lighting fixture connected to the inverter.
Both forms rely on stored energy from batteries. When normal power is supplied the batteries are connected to a charger which supplies constant current to ensure they are maintained at full capacity. Upon loss of building power, the transfer switch connects batteries to lamps in the emergency fixtures. In that event, the Life Safety Code stipulates that the amount of battery energy available must be sufficient to operate all emergency lighting lamps for a minimum of 90 minutes, after which the battery terminal voltage must be no less than 87.5% of the rated battery voltage, with the lamps remaining on. This performance requirement is strictly regulated under Underwriters Laboratories (UL) Standard 924 for Emergency Lighting and Power Equipment, which is based on criteria enumerated in LSC 101.
Operating conditions and maintenance problems concerning the two forms are as follows:
Unit Equipment: Batteries most commonly in use today for unit equipment emergency lighting products are Sealed Lead Acid (SLA), Nickel Cadmium (NICAD) or Nickel Metal Hydride (NIMH). Over time, the amount of stored energy in all types of battery will decrease, to the point when a fully charged battery is no longer able to meet the minimum power requirements for emergency operation, and they must then be immediately replaced. The typical average life of SLA batteries is 4 years; that of NICAD or NIMH batteries may be slightly longer. If the ambient temperature around a battery is elevated, as frequently happens in certain building installations, battery life may be less than 4 years.
LSC 101 specifies that all emergency lighting equipment be tested monthly for correct operation of the battery and the three other functions listed above, following a brief battery discharge. Then, every year starting 12 months after installation the fixtures must be tested with a battery discharge of 90 minutes (or more if specified for certain occupancies) at full load. If any of the three functions listed fails, or any battery fails to meet the 87.5% voltage minimum after 90 minutes, the fixture is in violation of the Life Safety Code, must be repaired or replaced to correct the fault, and retested to confirm proper operation. Results from these tests and/or corrections are to be recorded in writing, and the report must be available for inspection by the AHJ at any time. It is therefore important for the facility owner to be vigilant in reviewing the status of emergency lamps and the ability of batteries to maintain the 90 minute discharge.
The problem of review and inspection of unit equipment has been recognized in the industry and products have been developed to perform automatic, self-testing diagnostics of batteries and lamps, typically using a color-coded warning light on the fixture, or in some cases by incorporating a transmitter using WIFI to transfer diagnostic data from multiple fixtures to a central site. While these solutions may help the facility manager to identify equipment with bad lamps or batteries, they are expensive to install and do nothing to reduce the cost of replacing components found to be faulty, which is by far the largest portion of total maintenance expense.
Replacement of batteries and lamps in unit equipment is labor intensive because each fixture with a failed component must be accessed (most often requiring a ladder or a portable lifting system for fixtures in high locations), dismantled, have wiring disconnected, the battery, lamps or other components of the charging mechanism or the transfer switch replaced with new components, followed by reconnection, reassembly and testing. In many products, the battery is part of a package that includes the charger and transfer switch (known as an “emergency ballast’/) which increases the value of the material requiring replacement. In addition, typical batteries or emergency ballasts are manufactured specifically for the fixture and are thus not readily available as a stock item from electrical distributors; they must be carefully identified by part number and purchased direct from the factory or through a specialized supply service.
As described, total cost for routine maintenance of unit equipment for any facility can be substantial, especially in cases where large quantities of fixtures are installed. For example, unit equipment in a typical high school may contain more than one thousand batteries.
Inverters: An inverter may be supplied in a wide range of power capacities, from small models that supply one or a small number of lighting fixture with emergency power, to central power systems that can supply all fixtures throughout a large building. All inverters include a battery charger, a transfer switch and for emergency operation, an electrical circuit to convert DC power supplied from batteries into AC power for the lighting fixtures. The converter circuits are relatively complex and especially in larger machines, expensive. Frequently, multiple batteries are installed in larger machines and connected in series to produce high DC voltages, from 48V to 120V or more. Because of the inherent danger associated with high DC voltages and complex wiring schemes, manufacturers of such equipment usually require installation and setup by factory trained mechanics. Maintenance requiring replacement of batteries is also required to be carried out by factory technicians or electrical contractors with specific experience or training with this type of equipment.
Typical fixtures connected to inverters are designed for general lighting under normal conditions and as such, the lumen output, lamp power and beam spread patters are not optimized for emergency lighting. LSC 101 stipulates that emergency lighting must produce uniform illumination at a specified brightness level from 5 to 50 times lower than general lighting, along a path of egress, therefore an elongated beam spread concentrated along the egress pathway is desirable. However general lighting fixtures are designed to produce lighting over as large an area as possible, and most produce generally circular patterns, not elongated beams. The high power lamps used in these fixtures require far more battery power than lamps designed for emergency lighting. General lighting fixtures with multiple lamps can be configured to operate with a reduced number of lamps for emergency operation, thus saving battery energy, but that cannot be done with single-lamp fixtures.
As a result, general lighting fixtures operate at higher power than is required by the Code, requiring larger, more expensive batteries compared to a central power system for fixtures designed specifically for emergency lighting. Also, more fixtures with circular lighting patterns are required, compared to those with optical means designed to produce an elongated beam spread.
Lamps in use for general lighting may operate an average of 4,380 hours per year (12 hrs/day for 365 days). The most common type of lamps in use today are fluorescent, with an average life of about 15,000 hours or less. Therefore, many lamps will require replacement every 3-4 years and those connected to the emergency circuit will require thorough inspection and regular replacement to maintain code compliance.